The present invention relates to an apparatus for coating a substrate with a fluid, which in particular may be a dispersion or a suspension of a coating substance in a vaporizable carrier fluid, by means of a system of nozzles provided with at least one two-substance nozzle for the intermittent discharge of the fluid and the discharge of a gas.
Apparatuses of this kind are utilized, by way of illustration in so-called ink-jet printers, in particular, in "large character printing".
Moreover, such apparatuses can be employed in microdosaging and, in particular, for adding an active substance to a carrier, by way of illustration a tablet.
Another important use of such apparatuses is coating a pressing chamber with a lubricant: by way of illustration in the manufacture of tablets in human and/or veterinary medicine, of catalysts and various foodstuffs it is necessary to coat the top die, respectively the male mould, and the bottom die, respectively the female mould, with a lubricant in order to facilitate the pressing process as well as the ejection of the tablet following termination thereof.
DE-OS 27 17 438 proposes spraying the lubricant onto the pressing tools. Further details concerning the process described therein can be found in the article "Pre.beta.kammerbeschichtung, ein Beltrag zur Optimierung der Tablettenherstellung" (Pressing Chamber Coating, an Aid in Optimizing Tablet Production), published in Pharm. Ind. 50, 7, 839-845 (1988) or DE 39 02 293 A1.
The first figure of this article depicts a pressing chamber coating apparatus on which the generic part of hereto is based. In this apparatus a system of nozzles is employed that is provided with a two-substance nozzle from which the lubricant mixed with air emerges intermittently. For this purpose, the lubrication medium and the air are fed in doses alternately one after the other into the antechamber of the nozzle.
Although this state-of-the-art apparatus permits drastic reduction of the lubricant needed per pressed piece to amounts ranging from 0.01 to 0.01 mg per pressed piece, an element of the present invention is understanding that this state-of-the-art apparatus, too, still has a substantial drawback which prevents further reduction of the amount of lubricant used per pressed piece:
In this apparatus, application of the lubricant occurs essentially on the bottom surface of the male mould and the female mould, respectively the bottom die; an element of the present invention is, however, comprehending that the lubricant is particularly needed along the peripheral edge of the tablet, i.e. of the female mould, and at those sites where only relatively little lubricant is applied in the state-of-the-art apparatus. Thus, in this apparatus more lubricant is applied to the bottom surfaces than is necessary if the amount of lubricant is optimumly dosed along the peripheral wall of the pressing chamber (i.e., female mould).